1. Field of the Invention
The present invention relates to the field of the domestic and industrial water supply as well as to the field of the irrigation and is specifically concerned with the construction of floating apparatus for clarification of water from suspended particles directly at the point of its intake from a surface basin. Such an apparatus is particularly useful under the conditions of pre-clarification of high-turbidity water employed for the domestic water supply.
2. Description of the Prior Art
In modern practice, the pre-clarification of water from solid particles suspended therein is generally accomplished at shore water treatment facilities (settlers, clarifiers, drum screens, microfilters, etc.)
The pre-clarification of water at the shore facilities involves a problem of collection, processing, and utilization of the sediment, including the construction of sludge accumulators for dewatering the sediment and the construction of systems for the re-use of water clarified in a sludge accumulator.
The water treatment procedure at the existing facilities generally includes no direct clarification of water at the point of its intake from a surface water source, with the result that the solid particles suspended in the water flow give rise to an abrasive wear of the pumps installed on the water intake means. The same cause results in clogging of gravity-flow and distributing pipelines and receiving chambers of the shore water treatment facilities. This adverse effect is especially pronounced at a high content of suspended particles in the intake water and entails additional jobs for maintenance of the pumps and pipelines.
It has been propesed to employ submerged settlers for clarification of water at the point of its intake from a surface water source (E. S. Posgate. Submerged Enclosures May Help Sink Plant Problems. "Water and Wastes Engineering," 1977, vol. 14, No. 9, pp. 127-133).
Such a settler is arranged in a dome-shaped container submerged into a basin and retained at a predetermined depth with the aid of ropes secured at the bottom of the basin. The settler accomplishes a primary clarification of water, whereupon the latter is via a pipeline delivered to the shore water treatment facilities for a further treatment.
The operation of a settler of such a type involves the following substantial problems.
First, a continuous supply of air into the dome-shaped container is needed to protect the container from being ruptured by hydraulic shocks, and hence the water treatment facility must be equipped with air compressors.
Second, such a settler requires the use of hydraulic dredges for periodical removal of the sediment accumulating on the bottom of the container, which complicates the operation of the water treatment facility and raises the water treatment cost.
Third, the preventive maintenance and repair jobs on the settler call for the services of divers and for specialized tools.
And fourth, such settlers, while being of a considerable volume, offer but a relatively low capacity.
Due to the above disadvantages, submerged settlers have found no application in the water treatment technique.
Also known in the art is a floating apparatus for clarification of water (see U.S. Pat. No. 3,613,889, U.S. Cl. 210-84), which comprises a floating means whereon a settler and a piping for discharge of clarified water are mounted. The settler is installed in an enclosure and includes tubes disposed at an angle to the horizontal and defining a plurality of parallel passages in the settler. The passages are open at both ends for passing a liquid, in particular waste water therethrough, in an upward flow. The tubes are secured in the enclosure by their top ends so that they form a bottom of the enclosure, owing to which the clarified water collects in the latter.
The apparatus is arranged in a stationary reservoir wherein water being treated is supplied from a basin. As the water moves up the settler tubes under the laminar flow conditions, a gravity separation of phases takes place: solid particles suspended in the water separate from the liquid and settle on the lower inside surface of the tubes. The sediment thus formed slides to the bottom of the reservoir in a counterflow with respect to the direction of the water flow, while the clarified water is discharged through the piping from the enclosure out of the reservoir for a further treatment.
The practical employment of this prior art apparatus presents certain problems.
Inasmuch as the collection of the clarified water is accomplished in the enclosure locally, namely at the point of disposition of the inlet opening of the discharge piping, there exists no uniform collection of the clarified water from all the passages of the settler, which fact shows up as dissimilar water flow velocities in the passages. This impairs the degree of water clarification and results in nonuniformity of contamination load on the settler tubes, and hence upsets the process of an uniform removal of the sediment therefrom.
The nonuniformity of water collection rises with decrease in the height of the water column in the enclosure above the settler surface and with increase in the settler area.
Variations of the water level in the reservoir bring about pulselike changes of the water column height and changes of the water flow rate through the discharge piping. This upsets the hydrodynamic conditions in the settler passages, with the result that the settled particles from some of the passages are carried over into the space of clarified water. The above factors prevent a normal run of the water clarification process and impair the quality of the water.
It should also be noted that this apparatus fails to solve the problem of water clarification at the point of water intake from a basin, since it is intended for operation in a stationary reservoir with starting water, constructed on the shore as a component of a water treatment facility. Moreover, this apparatus, like prior art shore water clarification facilities, requires the use of special technical means for removal of the sediment from the reservoir, its processing and utilization.
Because the sediment from the settler passes into the reservoir and accumulates on the reservoir bottom, the volume utilization factor of the "floating apparatus-reservoir" arrangement, i.e. the ratio of the volume of the clarified water space to the overall volume of the arrangement, is relatively low.
An attempt to employ the above-described apparatus directly in an open flow, such as in a river, will bring about the following problems.
Because the velocity of flow in a river greatly (30-40 times) exceeds the velocity of water flow up the settler passages, eddy currents appear at the inlet openings of the passages, which upsets the uniformity of flow distribution among the passages.
In an open flow, the inlet openings of the passages get clogged with small floating objects (splinters, twigs, seaweeds) and also with fish fry, which progressively reduces the capacity of the settler and eventually renders it inoperative. It is for this reason that the apparatus is arranged in an enclosed reservoir rather than in an open basin.